1) Field of the Invention
This invention relates to bottom soils and filtering media that permits maintaining appropriate pH values during the rearing of fresh-water fish or hydroponic cultivation of plants and water tanks using such bottom soils and filtering media.
2) Background Art
During the rearing of fresh-water fish or hydroponic cultivation of vegetables, rice and other plants, it is necessary to maintain the pH value of water necessary for them within appropriate limits.
Fish are reared in various ways, such as breeding, fry raising, fattening, and keeping tropical fish. Hydroponic cultivation is done by, for example, burying cut pieces of stems or plant roots in the bottom soil under water. All of these are not done in systems where water is constantly supplied or discharged. They are performed in closed systems having water tanks or semi-closed systems where water is supplied from an external supply source and discharged as required.
When fish rearing and hydroponic cultivation are done in such closed or semi-closed systems, pH is likely to vary because water is changed infrequently.
In fish rearing, breathing and excretion of fish tend to make water increasingly acidic.
More specifically, carbon dioxide generated by breathing makes water acidic. Waste matters excreted naturally contain ammonia that is turned into nitric acid, by the action of microorganisms, that, in turn, makes acidic the water in the tank.
In the hydroponic cultivation in the aforementioned environments, physiological actions involving the excretion of acid materials from roots make water acidic. On the other hand, absorption of carbon dioxide through photosynthesis in water makes water alkaline, and absorption of mineral nutrition makes water acidic or alkaline. Thus, water becomes either acidic or alkaline depending on the level of these processes.
Suitable ranges of pH values for most fish rearing and hydroponic cultivation processes are known, whereas not much study has been made as to the compositions of bottom soils and filtering media for keeping appropriate pH values.
The object of this invention is to provide bottom soils and filtering media to keep appropriate pH values for fish rearing and hydroponic cultivation, water tanks using such bottom soils and filtering media, and methods of fish rearing and hydroponic cultivation using such bottom soils and filtering media.